1. Field of the Invention
The present invention relates to an electrostatic holding apparatus, and more particularly to an electrostatic holding apparatus useful for a process performed during fabrication of semiconductor devices, liquid-crystal devices, etc., which apparatus can strongly attract and hold a conductive, semiconductive, or insulating object by means of electrostatic force at any temperature ranging from a low temperature to a high temperature, and which enables easy attachment/detachment of the object. The present invention also relates to a method of producing such an electrostatic holding apparatus.
2. Description of the Related Art
Recently, processes for fabricating semiconductor devices, liquid-crystal devices, etc.; especially processes of drying etching, ion implantation, and vapor deposition, have become more and more automated and performed as dry processes. Under such circumstances, the number of fabrication processes performed under vacuum has increased.
Meanwhile, positional accuracy at the time of patterning has become more important, since the diameters of silicon wafers and glass plates serving as substrates have increased and the degree of integration of circuits and the degree of fineness of patterns have increased. Therefore, vacuum chucks have conventionally been used to transport wafers or to attract and fix wafers. However, vacuum chucks have the following drawbacks. Vacuum chucks cannot be used under a vacuum environment because of impossibility of creating a pressure difference. Although vacuum chucks can be used under a low-vacuum environment, a wafer subjected to suction undergoes a local distortion because the wafer is subjected to suction locally, with the result that accurate positioning becomes difficult. Therefore, vacuum chucks are not suitable for recently developed processes for fabricating semiconductor devices and liquid-crystal devices.
Recently, as a device that has overcome the above-described drawbacks, there has been widely noticed and put into practical use an electrostatic holding apparatus which transports and/or attracts and fixes a wafer by means of electrostatic force. In a recent process for fabricating semiconductor devices and liquid-crystal devices, with an increase in the degree of fineness of devices, the flatness of wafers and glass plates serving as substrates has become more and more important. Therefore, employment of electrostatic holding apparatuses has been considered, with a view toward performing a straightening correction for improving the flatness of wafers and glass plates. Also, since many processes are performed in a high temperature, corrosive gas atmosphere, an electrostatic holding apparatus formed of ceramics has been developed.
Two methods for producing such a conventional ceramic electrostatic holding apparatus have been proposed. In the first method, through printing or a like process, a conductive layer is formed on a substrate (insulator layer) formed of sintered ceramics, on which an insulating dielectric layer is formed through thermal spraying. In the second method, an insulating dielectric layer (a sintered body comprising 99% alumina) is bonded onto a conductive layer through used of adhesive.
Further, in recent years, an electrostatic holding apparatus having improved durability has been proposed (see Japanese Patent No. 2129621). This electrostatic holding apparatus is produced as follows. A conductive layer is sandwiched between a green sheet for an insulating dielectric layer and a green sheet for an insulator layer, both formed through tape forming, casting, or press forming, and the layer and sheets are superposed in an unfired state so as to become united, and then fired to obtain a sintered body serving as the electrostatic holding apparatus.
However, the electrostatic holding apparatus produced in accordance with the above-described manner has problems in that the electrostatic attraction surface has distortion and/or warping that is conceivably generated due to differences in coefficient of thermal expansion among the three layers, and in that since inter-layer delamination, cracks, and the like are generated in the sintered body, a sufficient electrostatic attraction force cannot be obtained, and withstand voltage is low.